FIELD OF THE INVENTION
This invention relates generally to integrated circuit (IC) packages and more particularly to a socket for use with testing IC packages.
In conducting a heat-resistance test of an IC package, called a burn-in test, it has been customary to place the IC package in a socket, in turn connected to a circuit substrate, such as a printed substrate, and then to place the substrate into a heating furnace to conduct the test to thereby determine whether or not the product is satisfactory.
Sockets for use in such IC package tests are known having the structures shown in FIGS. 1 and 2. The socket shown in FIG. 1 has a vertically movable cover 3 in which the IC package is inserted or removed by pushing down the cover. A plurality of contacts 4 having a prescribed pitch are mounted around the position of the base block 1 where the IC package is set. A connecting terminal 4b extends downwardly from a main body 4a. A support spring 4c extends upwardly and outwardly from each main body in a curved fashion approximately in the form of a U. One leg, attached to each main body, extends toward the base block while the other leg extends away from the base block and at its free end has a contact arm 4d extending back into the base block 1 and a lever part 4e which extends upwardly from the free end of the support spring 4c.
The distal free end of each lever 4e is pressed against the surface of a guide groove 3a which is formed on the lower surface of cover 3. When cover 3 is pressed down or push up, the distal end of each lever 4e is moved in dependence upon the moving inclined surface 3b of guide groove 3a.
In the construction shown in FIG. 1, if cover 3 is pressed down in opposition to springs 4c, lever parts 4e of contacts 4 are guided by the inclined surface 3b of guide groove 3a and move outwardly with the base part of the respective spring piece 4c as the fulcrum. Along with this, contact arms 4d rotate outwardly with the respective end of the spring piece 4c as the fulcrum, thereby moving away from the seat position of a lead of an IC package.
Thereafter, the main body 100 of an IC package is placed on the seat portion 1a of base block 1 and the downward force on the cover 3 is removed. As a result of this, the lever parts 4e of contacts 4 move and return inwardly as they are guided by the movable inclined surface 3b of the guide groove 3a. Concomitantly, the movable contacts 4d rotatably return inwardly, with their distal tip parts being biased into engagement with a respective tip of an IC lead 101 that has been placed on the seat position 1a from above. The compressive contact force applied to the IC leads is based on the spring force of the spring pieces 4c. In this manner, the IC package is installed in the socket.
When the IC package is to be removed from the socket, cover 3 is pressed down as in the previous case, the movable arms 4d of contacts 4 rotate outwardly and, after their distal tip parts separate and move outwardly from IC leads 101, the IC package is removed from the seat position 1a and downward force on cover 3 is then removed.
Regarding the socket shown in FIG. 2, on the other hand, the cover is rotatable toward and away from the base block with the cover being held in the closed state by a latch. As a consequence, the leads of the IC package that had been placed on the seat position of the base block are biased and engaged by respective contact parts of the contacts mounted on the base block of the socket.
In FIG. 2, a shaft 8 extends through a hinge part 5a formed at one end of base block 5 and a hinge part 6a formed on the base side of a cover 6 so that cover 6 is rotatable about the shaft in the direction of opening or closing the top of base block 5. A holding piece 6b is formed on the inner surface of cover 6 projecting along each of the four sides for holding each lead 101 of the IC package. Cover 6 is biased at all times in the opening direction by means of a spring 8 mounted on shaft 7.
A latch 10 is pivotably mounted on shaft 9 mounted on a side of cover 6 opposite hinge part 6a. A spring 11, provided on shaft 9, biases latch 10 at all times in the direction where base block 5 would be engaged with a step part 5c of base block 5.
The central portion 5d of the base block 5 is generally in the shape of a rectangular frame and a plurality of contacts 12, corresponding to the leads 101 of the IC package, are disposed around the periphery of the central portion. Terminal 12a of each contact 12 extends below the base block 5 to be connected to a circuit pattern of the circuit substrate (not shown in drawings) by means of insertion or soldering.
In the above described structure, after each lead 101 of the IC package is placed on a corresponding contact 12 with the leads 101 being positioned by boss parts 5e provided at four locations on the upper surface of base block 5, cover 6 is rotated around shaft 7 closing the top of the base block. As a result, a holding piece 6b of cover 6 engages each lead 101 of the IC package.
When cover 6 is further pressed, hook part 10a of latch 10 becomes engaged with step portion 5c of base block 5 fixing the cover to base block 5 in a closed state. Contacts 12 are pushed down along with leads 101 of the IC package by holding pieces 6b of cover 6 and engage leads 101 under a desired contact force because of the counter-force of the contacts, with a result that a satisfactory electrically conductive path is obtained.
After a heat resistance test of the IC package has been completed latch 10 is pivoted so that hook part 10a is disengaged from step portion 5c of base block 5 and cover 6 then rotates and returns to the open state by the spring force of spring 7 allowing removal of the IC package from base block 5.
The socket of the vertically movable cover type as shown in FIG. 1 has the following problems in spite of its advantage of being conducive to automating the mounting and removal of IC packages:
(1) There is a need to engage a respective IC lead 101 at a locus which is extremely close to the main body 100 of the IC package in order to minimize such problems as electrical loss, etc. However, the rotary movement of the contact arm 4d makes it difficult to have the tip of the movable contact 4d engage lead 101 at a position which is close to the main body 100 when the IC package is of the type shown in FIGS. 3 and 4 in which the leads extend straight out from the main body prior to forming and cutting of the leads, or at a location which is spaced from the tip of lead 101. Thus, even if it were applicable to the IC package in which leads 101 have been formed, as a general rule it is not useful with IC packages in which the leads 101 extend out in a straight line from the main body 100. PA1 (2) In the case of a socket of the vertically movable cover type according to the prior art, the route of the electric current is longer than desirable because of the structure of contact 4, with a consequence that the inductance of the circuit becomes greater thereby promoting cross talk between adjacent contacts and thus creating a problem of not being able to cope with the narrower pitch of the IC leads 101 used in more recent years.
Meanwhile, even though the prior art sockets of the rotating cover, as shown in FIG. 2, have the advantage of solving the above noted problems of the vertically movable cover type, its construction is not conducive to automation because of the rotational movement of the cover thereby bringing about a disadvantage in that IC package mounting and removal cannot easily be automated.